Throughout this application various publications are referenced by arabic numerals in parentheses. Full citations for these references may be found at the end of the specification immediately preceding the claims. The disclosures of these publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art to which this invention pertains.
In vertebrates, many different processes as diverse as growth, vision, and reproduction are vitamin A (retinol) dependent (5). Retinol is the source for specific derivatives, i.e., retinoids, which are adapted to specified functions, such as 11-cis retinal in vision (6) or 9-cis and all-trans retinoic acid for differentiation of a number of cellular systems (7). The general mechanism of action of retinoids presumably is connected with their specific binding proteins including nuclear receptor molecules that are involved in transcriptional regulation (8,9).
Retro-retinoids are characterized by a planar ring-to-tail configuration, rigidly enforced by the rearrangement of the carbon double bond system so as to fix the hexenyl ring by a double bond to the polyene tail. The first of the natural retro-retinoids to be discovered, 14-hydroxy-4,14-retro-retinol (14-HRR), plays a role in the regulation of lymphocyte proliferation (3,4).
A general feature of retinoids in biological systems is their association with intra- and extracellular specific binding proteins. These function as carriers for transport and for protection against oxidative degradation. In specific cases, i.e., all trans-retinoic acid, nuclear receptors, involved in transcriptional regulation, are activated after binding of the retinoid ligand. Although 14-HRR-specific binding proteins and respective nuclear receptors have not yet been demonstrated, the reversible inhibition of 14-HRR by its structural analog, anhydroretinol, implies their existence.
In serum-free, defined medium, growth of transformed human B lymphocytes and antigen-receptor-mediated activation of T lymphocytes is controlled by retinol in a dose-dependent fashion, the optimum concentration range being 2.times.10.sup.-7 M to 2.times.10.sup.-6 M (1,2). Retinol is enzymatically converted in lymphocytes and other cells into 14-HRR. 14-HRR substitutes effectively for retinol when a 1 to 5.times.10.sup.-8 M concentration of exogenous 14-HRR is maintained in the medium (4).
The hydrocarbon anhydroretinol (AR), first detected in 1939 in fish liver oils (10), is structurally closely related to 14HRR and was therefore tested for its effects on B cell proliferation.
Anhydroretinol, though a structural analog of 14HRR, has been discovered not to aid B cell proliferation but to reversibly inhibit retinol- and 14HRR-dependent effects and to block B lymphocyte proliferation as well as activation of resting T lymphocytes.